The present invention relates to determination of tear film lipid layer thickness.
Dry eye disease is most often caused by excessive tear film evaporation, leading to hyperosmolarity of the tear film, resulting in ocular surface inflammation and exacerbation of the problem. Excessive tear film evaporation is often caused by an abnormal tear film lipid layer, either in amount or in quality. The amount or quality of tear film lipid can manifest itself in changes in thickness of the lipid layer. Generally, a thicker lipid layer is associated with a normal tear film, whereas the opposite is often the case for dry eye. Present clinical measurements of the tear film lipid layer are for the most part qualitative or semi-quantitative in nature. Korb, in U.S. Pat. Nos. 8,591,033 and 8,585,204, disclose a quantitative method for measuring the thickness of the tear film lipid layer. However, this method does not measure the lipid layer over the central cornea where tear film thinning and breakup due to evaporation is maximal and where it is believed a better diagnosis of dry eye can be obtained. Huth, in U.S. Pat. No. 8,602,557 B2 (incorporated herein by reference in its entirety) also disclose a quantitative method for measuring the thickness of the tear film lipid layer as part of a method to simultaneously measure the tear film aqueous layer and the corneal surface refractive index. However, this method requires as long as 475 seconds to complete the calculations for a single tear film spectrum.